The use of double metal cyanide catalysts in the preparation of high molecular weight polyols is well-established in the art. For example, U.S. Pat. No. 3,829,505, assigned to General Tire & Rubber Company, discloses the preparation of high molecular weight diols, triols etc., using these catalysts. The polyols prepared using these catalysts can be fabricated to have a higher molecular weight and a lower amount of end group unsaturation than can be prepared using commonly-used KOH catalysts. The 'U.S. Pat. No. 505 patent discloses that these high molecular weight polyol products are useful in the preparation of nonionic surface active agents, lubricants and coolants, textile sizes, packaging films as well as in the preparation of solid or flexible polyurethanes by reaction with polyisocyanates.
An unfortunate result associated with the preparation of high molecular weight polyols using DMC catalysts is that DMC catalyst residues remain in the finished polyol. If not removed from the polyol, these catalyst residues tend to cause undesirable side reactions, thereby forming unwanted by-products which, in turn, cause odor and other storage problems.
Various solutions to the catalyst residue problem have been proposed. By way of illustration, U.S. Pat. No. 4,355,188 discloses that the removal of double metal cyanide catalyst residue can be accomplished by adding a strong base selected from the group consisting of potassium hydroxide, sodium hydroxide, potassium metal. and sodium metal, and incorporating an effective amount of ethylene oxide into the catalyst residue-containing polyol/alkali metal hydroxide mixture in order to convert the secondary hydroxyl groups of the polyol to primary hydroxyl groups. The process of the 'U.S. Pat. No. 188 patent has been found by the present inventors to not be effective in producing purified all-propylene oxide (i.e., ethylene oxide-free) purified polyols.
As another illustration, U.S. Pat. No. 4,721,818 discloses a process which comprises (a) incorporating into the catalyst residue-containing polyol an effective amount of an alkali metal hydride in order to convert the double metal cyanide complex catalyst into an insoluble ionic metal species separable from the polyol, and wherein the polyol hydroxyl groups are also converted to alkoxide groups, and (b) separating the insoluble ionic metal species from the polyol. Unfortunately, practical application of this process requires an intermediate step between steps (a) and (b) involving the incorporation of an effective amount of ethylene oxide into the catalyst residue-containing polyol/alkali metal hydroxide mixture in order to convert the secondary hydroxyl groups of the polyol to primary hydroxyl groups. Moreover, the process of the U.S. Pat. No. '818 patent has been found by the present inventors to not be effective in producing purified all-propylene oxide (i.e., ethylene oxide-free) purified polyols.
As yet another illustration, U.S. Pat. No. 4,877,906 discloses a complicated method involving (a) treating a DMC catalyst residue-containing polyol with alkali metal compound(s), (b) filtering and (c) treating the filtered polyol with a phosphorous compound to convert the soluble portion of the DMC catalyst residue into an insoluble portion, (d) filtering again, and then (e) recovering the polyol. This process is not as simple and straightforward as might be desired.
The processes disclosed in the above discussed patents have the disadvantage of being applicable only to specific polyols and utilizing treatment chemicals which themselves cause the formation of residues in the polyol. New approaches to providing catalyst residue removal that are inexpensive, generally applicable to all polyols, and do not themselves cause a residue problem would be highly desired by the polyol manufacturing community.